The present invention relates to a machine tool such as threading machine.
There is a type of a machine tool provided with a rotatable spindle having a cutting tool for cutting a workpiece.
Generally, the quality of the machining operation is affected by the occurrence of various faults, such as, cutting chips being caught between the workpiece and the cutting tool or a worn-out cutting tool.
It is known that, if a fault occurs while the machining tool is cutting the workpiece, a torque required to rotate the spindle is increased. Therefore, a conventional machine tool is arranged to detect a torque applied on the spindle while the spindle is rotating, thereby to determine that a fault has occurred.
Since the torque applied on the cutting tool may be affected by the acceleration and the deceleration of the spindle, it is necessary to detect the torque while the spindle rotates at a constant speed.
However, in some cases, such as in threading a short thread, the time interval while the spindle rotates at a constant speed may be relatively short. In such short time interval, the torque cannot be detected accurately.